For gasifiers for in-line gasification of slag-forming fuels, a known possibility is to delimit the reaction space by a multi-start spiral shaped coiled pipe diaphragm wall, also referred to as a cooling jacket. The cooling water which flows through the cooling jacket is fed in and out via connectors which are connected to the cover of the gasifier (FIG. 1). DE 202009012134 discloses an appropriate construction with four cooling water inlets and four cooling water outlets.
The increasing number of coils for larger gasifier capacity requires more connectors, which it is either impossible or illogical to arrange on the head of the vessel because of space limitations. Total emptying for the purpose of avoiding freezing up is not possible.
The nominal size of the cooling water pipes represents a further limiting factor in the dimensioning of the cooling jacket. As the reaction space is enlarged, with the objective of raising the capacity, the heat exchange area increases, with the result that a larger quantity of water is required to dissipate the amount of heat. An enlargement of the nominal size of the pipe diameter has the observable disadvantage that, on the one hand, the molten slag flows away less well at the tube wall and, on the other hand, the slag formation becomes less uniform, and overall becomes worse. Uniform slag formation is necessary in order to avoid local overheating and damage to the cooling jacket. As the nominal size is increased, a lower percentage of the water volume participates in the direct heat exchange, which can also promote local overheating.
The cooling water cannot be completely removed by the usual measures, such as draining off or “blowing out” using compressed air, so that in winter it is necessary to keep the circuit, the vessel, or its surroundings frost-free when taken out of service.
Inspection of the cooling jacket gap, or its replacement, involves extensive work, tests and dismantling, in particular at the connector bushes through the vessel's pressure shell. The challenge consists in being able to mount the upper vessel cover, which involves the demanding threading in of the forward and return flow pipes and making of the final welded seams with restricted ability to test them (vessel pressure testing). It is conventional, in accordance with the regulations (AD, ASME), that no more welding work is carried out after the vessel pressure testing.
Until now, when the gasifier capacity is increased the nominal size of the cooling jacket pipes has been increased, for the purpose of carrying away the additional quantities of heat.
A problem is that of designing an in-line gasifier with a liquid-cooled cooling jacket in such a way as to simplify the way the pressure vessel cover is mounted.